1. Field of the Invention
The present invention relates to a magnetic tape having an optical servo track. More particularly, the present invention relates to a magnetic tape having an optical servo track on the side opposite to the magnetic recording side.
2. Description of the Related Art
The recent expanding scale of the computer network and the importance of security for data management have been increasing the demand for a magnetic tape having an increased recording capacity for use as a medium for data backup. Approaches to high recording capacity are divided into improvement on recording density and extension of the tape length.
Since the tape length is limited by the capacity of a tape cartridge in which a roll of tape is put, extension of the tape length cannot be achieved but by reducing the tape thickness. Therefore, an increase in recording capacity attained by this approach is of necessity limited. With respect to the recording density, it is known that a magnetic tape has a lower recording density than a hard disk drive. A magnetic tape having serpentine track scanning particularly has a low recording density, which is due to the low track density. On the other hand a magnetic tape having helical track scanning, which uses a servo tracking system called ATF (automatic track finding), possesses a higher track density than the magnetic tape having serpentine track scanning.
Servo tracking systems have also been adopted to the magnetic tape having serpentine track scanning to improve the track density. Such servo tracking systems include an embedded servo system, in which servo signals are written on the same track as the data track on the magnetic recording side, and a system in which a track exclusive to servo signals is provided on the magnetic recording side. Japanese Patent Publication No. 82626/95 discloses a servo tracking system particularly useful where the pitch of data tracks is as small as several tens of microns, in which dedicated tracks for servo signals are provided on the magnetic recording side and a plurality of servo signal read heads are used for reading the servo signals. According to this technique, however, the number of servo signal read heads must be increased as the number of data tracks increases. Otherwise, the number of servo tracks should be increased. Like this, conventional servo tracking systems use the same side of magnetic recording as used for data recording, which means that the data recording area is reduced accordingly. This disadvantage is conspicuous in the servo tracking system of Japanese Patent Publn. No. 82626/95 when a track density is as high as about 30 tpmm (tracks per mm) or even more.